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Microbiology > M3 Gram Positive Bacilli > Flashcards

M3 Gram Positive Bacilli Flashcards

1
Q

Where is Bacillus spp.and/or the Bacillaceae family generally can be found?

A

Bacillus spp.:

  1. Found widely distributed in nature (in soil and water) as vegetative cells and spores.
  2. Dried foods (spices, milk powders, flour) are often contaminated with spores.
  3. Frequent colonizers of skin, GI tract, and respiratory tract of humans.
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2
Q

Is it important to identify Bacillus spp.?

A

Most of the time it is more important to rule out Bacillus anthrasis.

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3
Q

What are the family traits of Bacillaceae family: Bacillus, Brevibacillus and Paenibacillus?

A

Bacillaceae family traits:

  1. Aerobic and facultative ANO2 or strictly ANO2.
  2. Large G+b
  3. Spore forming
  4. Catalase positive
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4
Q

What is Bacillus spp. used for the production of?

A

Antibiotics
E.g.
Bacitracin from Bacillus subtilis
Polymyxin from Bacillus polymyxa

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5
Q

What type of sickness can Bacillus cereus cause and why?

A

Bacillus cereus produces enterotoxins and pyogenic toxins which cause food poisoning resulting in abdominal pain and watery diarrhea (8-16 ours) after eating contaminated food) or profuse vomiting (1-5 hours after eating contaminated food).

Contaminated food is a concern because their spores can survive normal cooking procedures so when food is stored improperly the spores can germinate and the vegetative cells multiply.

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6
Q

What type of opportunistic infections can be caused by Bacillus cereus?

A

Bacillus cereus can cause:

  1. Serious eye infections (endophthalmitis) as a result of trauma.
  2. Infections from IV drug use due to skin contaminations.
  3. Blood infections due to skin contaminations.
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7
Q

Is Bacillus subtilis important to identify in the clinical microbiology laboratory and why not?

A

Bacillus subtilis is a common environmental contaminant.

Unless this organism is found in a sterile site such as in bacteremia, the clinical microbiology laboratory typically does not identify it.

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8
Q

Where is Bacillus anthracis found?

A

Bacillus anthracis is found in the soil, even in Manitoba (farms)!

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9
Q

What is the result of a Bacillus anthracis infection?

A

Bacillus anthracis infections may result in death

due to the production of antiphagocytic capsules and exotoxins that mediate cell and tissue destruction.

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10
Q

What makes Bacillus anthracis a “good” agent for biological warfare or terrorist attacks?

A

Highly resistant to heat and desiccation.

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11
Q

What are three forms of anthrax?

A
  1. Cutaneous anthrax - site of spore penetration –> can form a necrotic lesion known as an eschar
  2. Pulmonary anthrax - inhalation of spores
  3. Gastrointestinal anthrax - ingestion of spores (Injection)
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12
Q

What makes one suspect Bacillus anthracis when doing a blood agar plate?

A

If the blood agar shows:

  1. Non-hemolytic colony with “Medusa head” formation (comma-shaped protrusions).
  2. Ground glass appearance & spikes (If you lift with a loop it stays up).
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13
Q

What are routine tests performed on Bacillus spp. to identify it?

A
  1. Blood Agar plate - look for dry gray to green frosted glass appearance.
  2. Gram stain - Large g+b with square or concave ends containing endospores (appears as intracellular non-staining ovoid ares).
  3. Catalase - Pos
  4. Motility
    Bacillus cereus is Pos
    Bacillus subtilis is Pos
    Bacillus anthracis is Neg
  5. Penicillin Sensitivity/Resistance; B anthracis is Penicillin S.

Then sent to reference lab for final identification because they require a bicarbonate base in the biochemical tests and Bio-safety level 3.

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14
Q

What are Corynebacteriaceae family traits?

A
  1. Facultative anaerobes (means can grow with O2 or without O2).
  2. Short G+b
    - Irregular rods whole long edges are curved, not parallel.
    - Coryneform rods - club-shaped bacilli
    - Diphtheroid arrangement: palisades of parallel cells (like
    a fence), V or L shaped pairs of bacilli and clusters.
  3. Do not form spores
  4. Do not branch
  5. Catalase positive.
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15
Q

When is a Corynebacterium spp. not part of the normal flora?

A

When it is Corynebacterium diptheria when isolated from the nasopharynx.

In that case it should be considered potentially pathogenic.

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16
Q

What Corynebacterium spp. may cause UTI’s and who is the at risk population?

A

Corynebacterium urealyticum may cause UTI’s in immunocompromised patients.

17
Q

What type of infection can Corynebacterium macginleyi cause?

A

Can cause eye infections.

18
Q

Which species of Corynebacterium result in opportunistic infections on the skin of hospitalized patients?

A

Cornyebacterium jeikeium

19
Q

What bacteria is associated with ulcer in individuals who farm?

A

Corynebacterium ulcerans.

20
Q

How are toxigenic strains of Corynebacterium diphtheriae produced?

A

By a bacteriophage (virus)that integrates into the bacteria.

21
Q

What happens when C. diphtheriae is made toxigenic?

A
  1. Pharyngitis with inflammatory grey pseudomembrane. It can obstruct the respiratory tract.
  2. Infection spreads and can damage other organs such as the heart if released into the bloodstream and lead to cardiac arrest (10-30% mortality).
  3. Non-healing ulcers.
  4. Cutaneous infection.
22
Q

How is C. diphtheriae transmitted?

A

The bacteria may be transmitted through droplet infection by person to person contact.

23
Q

What are the routine tests for Corynebacterium spp. to identify it?

A

Routine Tests for Corynebacterium spp.:

  1. Blood Agar colonial morphology: dry gy, non-hem or hem
  2. Gram: Small g+b (typical “diphteroid”)
  3. Catalase: mostly ++
  4. CTA sugars
  5. Urease: Neg (except for C. ulcerans and C.urealyticum).
  6. Penicillin or Vacomycin used for ID: Sensitive (except for C. jeikeium which is Resistant)
24
Q

Where is Listeria monocytogenes typically found?

A

Widely distributed in nature, especially in soil, decaying vegetable matter, food, and raw milk.

Also processed poultry, meat, raw milk, cheese, ice cream, raw fruits and vegetables.

25
Q

What infection are newborns susceptible to?

A
  1. Listeriosis - bacteremia and meningitis can occur in susceptible patients (especially conditions that lower cell-mediated immunity).

Newborns are particularly vulnerable to this infection.

26
Q

What bacteria infection can occur in utero for fetuses?

A

Granulomatosis infantiseptica; Listeria monocytogenes is one of the few organisms that can cross the placenta and can get this infection in utero. Causes stillbirth.

27
Q

Besides in pregnancy and newborns where else can Listeriosis be observed clinically?

A

People with AIDS
Renal transplantation with high-dose steroids.

L. monocytogenes can cause meningitis (secondary) in neonates and immunosuppressed adults.

28
Q

What are Listeria monocytogenes virulence factors?

A

Virulence of L. monocytogenes:

  1. Intracellular pathogen infects macrophages.
  2. Exotoxin Listeriolysin O, binds to membrane cholesterol and disrupts phagolysosomes of infected macrophages.
  3. Act A facilitates cell-to-cell spread.
29
Q

What are two modes of infection of Listeria monocytogenes?

A

L. monocytogenes two modes of infection are:

  1. Ingestion of contaminated food.
  2. Transmission to fetus in utero if mother has bacteremia caused by Listeria monocytogenes (crosses the placenta).
30
Q

What are the routine tests for Listeria monocytogenes to identify it?

A
  1. BA colonial morphology: sm trans with narrow zone β-hem
    Resembles Group B strep
  2. Gram Stain: g+b or g+cb
  3. Catalase: Pos
  4. Ferments glucose
  5. Bile Esculin: Pos
  6. Motility: Pos (End over end – “tumbling”, Enhanced at cooler temps (20-25degC), Umbrella pattern in soft agar)
31
Q

Where is Lactobacillus spp. typically found as normal flora?

A

Found in the mouth (in both saliva and plaque), the intestinal tract, the vaginas of humans and other mammals and a variety of food products.

32
Q

What do Lactobacillus spp. look like on a gram stain?

A

Lactobacillus spp. are long thin gram positive bacilli, sometimes slightly bent or coryne-looking.

33
Q

What are routine tests to identify Corynebacterium diphtheriae?

A

Routine Tests:
1. If Gram smear is suspicious – sub to BA and Tinsdale
BA – gy trans or white, non-hemolytic colonies up to 2 mm in size after 18-24 hours in 5% CO2 at 35oC
2. Tinsdale Agar
a) Potassium tellurite is a selective agent
b) Cysteine and sodium thiosulphate are indicators
- Black colonies form due to the presence of tellurite reductase
- Have brown halo due to cystinase
- Staphylococcus and Proteus can form black colonies as well, but not brown halo
3. Elek Assay for Diphtheria Toxin

Microbiology (13 decks)

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